Repeat statements whilst a continuation condition is met
  While Expression do Statement;
The While keyword starts a control loop that is executed as long as the Expression is satisfied (returns True).
The loop is not executed at all if the expression is false at the start.
You need Begin or End markers if multiple statements are required in the loop.
It is used when it is important that the statements are at only executed when necessary.
Related commands
Begin Keyword that starts a statement block
Boolean Allows just True and False values
Do Defines the start of some controlled action
End Keyword that terminates statement blocks
For Starts a loop that executes a finite number of times
Repeat Repeat statements until a ternmination condition is met
Until Ends a Repeat control loop
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Example code : Display integer squares until we reach 100
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
  Forms, Dialogs;
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
Form1: TForm1;
{$R *.dfm} // Include form definitions
procedure TForm1.FormCreate(Sender: TObject);

  num, sqrNum : Integer;

  num := 1;
  sqrNum := num * num;

  // Display squares of integers until we reach 100 in value
  While sqrNum <= 100 do
    // Show the square of num
    ShowMessage(IntToStr(num)+' squared = '+IntToStr(sqrNum));

    // Increment the number

    // Square the number
    sqrNum := num * num;
Hide full unit code
   1 squared = 1
   2 squared = 4
   3 squared = 9
   4 squared = 16
   5 squared = 25
   6 squared = 36
   7 squared = 49
   8 squared = 64
   9 squared = 81
   10 squared = 100
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